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Design for Manufacturing: Concept to Reality

Saturday, 01 December 2012

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Design for Manufacturability (DFM)
is a well-established practice,
essential in realizing the transformation
of new product concepts
into mass-produced medical devices. And
yet, all too often issues that could have
been avoided are identified very late in
the process and impact production costs
and schedules. This suggests that key
DFM principles are often underutilized
in practice and not applied consistently,
or to the degree necessary, to avoid these
negative implications.

This article discusses three DFM-based
best practices that help create conditions
for success as manufacturing partners
work with device designers towards
a common goal. Engaging key stakeholders
in an organized team from the
very start of a project, conducting a thorough
feasibility study, and implementing
the proper quality tools will ensure that
a device design is reliable, manufacturable,
and acceptable to the physician
or end user.

Integrated Product Development:
One Team, Multiple Disciplines

The first and most important element
of DFM is a truly integrated multi-disciplinary
product and design development
team. Good collaboration here
can help ensure that elegant engineering
solutions are practical to manufacture
from a cost or materials standpoint,
and suit the end user. An integrated
team also helps reduce the risk of a
“silo” approach and an overemphasis of
any one element, while other design
considerations are overlooked.

A senior staff engineer from one device
manufacturer said the level and degree of
the DFM teams vary, but may involve representatives
from product management,
quality and design engineering, regulatory,
packaging, purchasing, calibration,
prototyping, post-market, and others as
required. He added, “We have a strict
procedure in place based on the product
and production line. The team must be
approved at the project charter stage.”

All critical customer requirements must
be clearly established during initial team
meetings, as total project lifecycle costs
and speed to market are often dictated
early on in the process. A good interdisciplinary
team considers important details
such as performance characteristics, cost,
timeline, clinical needs, and regulatory
requirements. (See Figure 1)

“From the design phase, suppliers who
are critical to the project’s success should
be included in the discussions, and the
sooner the better,” said a senior staff engineer.
“We receive great input from our
suppliers in their fields of expertise and
having a good partnership with the supplier
ensures the launch is successful.”

Consulting with key suppliers early
can avoid costly rework later down the
line. For example, Precipart recently
prepared a feasibility study for a tight
tolerance gear assembly that identified
an opportunity for performance
im provement of a medical imaging
device by recommending bench assembly
and light run-in to create the
contact pattern on a helical gear.
Improving gear backlash by approximately
.002" would significantly
improve the durability and performance
of the device. (See Figure 2)

The Feasibility Study:
Charting the Course for Success

A comprehensive feasibility study
examines the key specifications throughout
the life of a project and requires the
team to thoroughly review and consider
all potential design issues from the project’s
beginning. A thorough feasibility
study will provide information on a
number of aspects crucial to the success of a product. Some aspects to consider
include:

Materials Selection: This is crucial because biocompatibility issues often combine
with metallurgical and process
challenges to impact manufacturing
techniques downstream. The need for
biocom patible materials may require
changes in manufacturing approaches. For
example, titanium screws for a prosthesis,
while biocompatible, are difficult to injection
mold and may require machining that
adds complexity and cost. Hip and knee
replacements require both costly highgrade
materials and complex post-machining
processes such as coatings or polishing.
Ceramics are biocompatible but may be
more expensive in high volumes. The
grade of ceramics can also make a difference,
as in the recent case of a cardiac
rhythm management device that had a
high failure rate because cracks appeared
during post-fabrication brazing. Substituting a higher, more heat-tolerant grade
proved to be more cost-effective in the long
run because of higher throughput.

A feasibility study should also consider
the tolerance of materials for post-fabrication
treatments, such as deburring and
brazing. Materials, such as titanium, can
cause laser markings on surgical instruments
to smear or be rubbed off. Keeping
them legible may require additional
processes, such as coating or embossing.
Choosing the right material can also
reduce fabrication steps.

Manufacturing Processes: Alternative
manufacturing processes are almost
always available but the trade-offs need
to be weighed between speed and cost.
For example, multiple machining steps
might be replaced by ceramic or metal
injection molding for some components.
Ma chined components can be
used for initial design and the proof of
concept phase, with injection molding
substituted during production.

Application demands often determine
the processes used. Injection molding
may be the most economical way to produce
gears in volume, but if the device
requires high torque, machined gears
may be required to maximize durability.
Similarly, designs can be changed early in
the process so that parts are produced by
off-the-shelf tooling instead of using more
costly specialized machinery or tools.

Finishing Processes: A component’s finish
can have a substantial impact on
durability, service life, and clinical performance.
Poorly finished parts are a frequent
cause of rejection and production
delays. Some clinicians demand a pristine-
looking reflective mirror finish,
which may require specialized metals,
surface treatments, polishing, or blasting.
Other instruments need duller finishes
to reduce glare during surgical
procedures.

The need for easy sterilization is
another design factor that often guides
DFM teams in selecting materials and
processes. Where instrument life and
durability is an issue, the team may recommend
electropolishing or the use of
anodized metal. The look and feel of a device or instrument may make the difference
in acceptance by end users.

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